1. Field of the Invention
This invention relates to methods for preparing polyhaloaromatic carboxylic esters, some of these esters per se, and the use of some esters as flame retardants and/or processing aids.
2. Statement of Related Art
A number of processes have been developed for the preparation of diesters of the phthalic acids and phthalic anhydride from alcohols using traditional strong acid esterification catalysts, such as sulfuric acid, p-toluenesulfonic acid, hydrochloric acid, etc. However, when the aromatic rings are polyhalogenated, complete esterification becomes slow and difficult, resulting in low yields and poor product quality which make these processes commercially unattractive.
Pape, Sanger and Nametz (J. of Cellular Plastics, November, 1968, p. 438) discloses that diesters of tetrabromophthalic anhydride can be prepared only with great difficulty and in low yields. Pape, et al., used epoxides to convert the free-carboxyl group of the intermediate monoester to a hydroxy-substituted ester.
Spatz, et al., (I & EC Product Res. and Dev., 8, 391, 1969) used phosphoric acid as a catalyst to prepare the di-2-ethylhexyl ester of tetrabromophthalic acid with only 60% yield. Substantial decarboxylation of the intermediate half-ester was also observed.
Baldino and Feltzin in U.S. Pat. No. 3,929,866 reported the preparation of diesters from alcohols containing at least 3 hydroxyl groups; however, no products were isolated and no yield details are given.
Finley in U.S. Pat. No. 4,375,551 prepared allylic esters of tetrabromophthalic anhydride by first preparing the half-ester and then converting the half-ester to the sodium salt which was then treated with allyl chloride in the presence of phase transfer catalysts.
The use of metallic salts of tetrachlorophthalic anhydride to prepare diesters has been documented by several workers. Nordlander and Cass (J.A. Chem. Soc. 69, 2679 (1947)) disclose that diesters of tetrachlorophthalic acid have been prepared by reacting a metallic salt of the acid with an alkyl halide or sulfate, or by reacting tetrachlorophthalyl chloride with a sodium alcoholate. Nordlander et al. also disclose the direct esterification of tetrachlorophthalic anhydride using acid-catalyzed, non-catalyzed high temperature, and base-catalyzed high temperature reactions. The acid-catalyzed reaction yields ranged from poor to fair (10 to 70%).
Lawlor (I. & EC, 39, 1419 (1947) reported low yields of diesters could be obtained from either the sodium or silver salts of the intermediate half-ester of tetrachlorophthalic anhydride or from the acid chloride, tetrachlorophthaloyl chloride.
Nomura, et al., in Japan published Patent Application 75-05701 discloses the use of alkyl titanates together with alkali or alkaline earth metal salts (hydroxide, carbonate, bicarbonate, or salt of organic acid) for the esterification of tetrabromophthalic acid or anhydride with alcohols to produce the corresponding diesters. These alkali or alkaline earth materials are an essential part of the Nomura, et al., catalyst system, whether added together with the alkyl titanate or at different times during the process in order to obtain products having low acid numbers.